Combine-harvesters are large machines which harvest grain from a field, thresh it and clean it. A combine-harvester includes a number of adjustable elements, such as the size of the openings of a threshing basket or of a separating screen, the size of a threshing gap, the speed of a threshing drum, the speed of a cleaning blower or the position of slats of a sieve. The optimum operating parameter of said elements depends on the type of harvested crop and the characteristics thereof and can change over time. The adjustment of said parameters is usually carried out by the operator of the combine-harvester on the basis of operating instructions or his experience or it is carried out automatically using values which are filed in a memory and which are called up by the operator as a function of the current conditions of the surrounding area and of the harvested crop. In the past, many sensors have been proposed to detect the characteristics of the harvested crop (such as capacitive moisture sensors, cameras and near infrared spectrometers) in order to detect harvested crop characteristics on board the combine-harvester and to give the operator an indication concerning the characteristics of the harvested crop present at that time after processing in the harvesting machine, on the basis of which he (or an independent control means) is able to modify parameters of the processing process in the harvesting machine. Thus, for example, he can enlarge the threshing gap and reduce the speed of the threshing drum if the proportion of broken grain is too high.
A camera, which, for example, takes an image of the cleaned grain before it passes into the grain tank, or an image of the material in the returns conveyor which supplies harvested crop from the rear end of a sieve back to the threshing operation or to a separate finishing thresher, is particularly suitable to obtain information for the manual or automatic adjustment of parameters of the processing process of a combine-harvester. As an unprocessed image is hardly meaningful in particular to operators with little experience, the image, as a rule, is processed by means of an electronic image processing system in order to indicate to the operator, on the one hand, certain particles, such as broken grain or contaminants in the image shown of the harvested crop in colour or highlighted in another manner and, on the other hand, to be able to display quantitative sizes (for example with regard to the proportion of broken grain and/or contaminants). The quantitative sizes can, as already mentioned, be used for the manual or automatic adjustment of parameters of the processing process in the harvesting machine.
EP 2 057 882 A2 describes a combine-harvester with such an image processing system which initially carries out a brightness match on the recorded digitalized image data. The image is then subjected to segmenting, which can be targeted at individual objects and/or individual object edges. In the case of such targeted segmenting, the image is divided into individual objects defined by brightness or colour values which are identical per se. By way of comparison between the brightness of the respective region and a required value or a mean value for the brightness of the image, it is concluded whether the region represents a broken grain. The area of the broken grain is determined by counting the pixels of the region and the proportion of broken grain is evaluated by way of comparison with the number of pixels in the image. Edge-oriented segmenting serves to identify broken grain and is based on an evaluation of the lengths of the boundaries of the individual objects. Where the object is sufficiently large, it is assumed that it is a short piece of straw. The areas of the objects identified as short straw are also compared in relation to the size of the entire image in order to determine the proportion of contaminants. The assignment of the image objects to the “broken grain” or “short straw” classes is effected accordingly simply by way of the brightness of the individual objects or of their length. In this connection, inaccuracies can hardly be avoided because, for example, it is not possible to determine short straw particles which are smaller than the grains. In an analogous manner, broken grains with broken areas which do not lie head-on to the camera are not differentiated from intact grain.
U.S. Pat. No. 5,917,927 A1, which is viewed as generic, describes a stationary arrangement for determining the proportion of broken grains of rice where the dimensions (length, width and area) and possibly also other dimensions of each grain are determined from the image taken. Classification of the grain is effected by comparison with data from a table, in which simulated or currently measured data for grain is filed, which is called up by way of combinations of features of the respective grain to be inspected. Here too the classification is effected only by way of the dimensions of the respective object, which involves the disadvantages already mentioned in the preceding paragraph.